Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.34

3.9.3.34

ayuṅgā-ayuṅgā ekadhanā bhavanti | trayo vā pañca vā pañca vā sapta vā nava vā nava vaikādaśa vaikādaśa vā trayodaśa vā trayodaśa vā pañcadaśa vā dvandvamaha mithunam prajananamathā tha eṣa eko 'tiricyate sa yajamānasya śriyamabhyatiricyate sa vā eṣāṃ sadhanaṃ yo yajamānasya śriyamabhyatiricyate tadyadeṣāṃ sadhanaṃ tasmādekadhanā nāma

The Ekadhana pitchers are always of uneven number,--either three, or five, or seven, or nine, or eleven, or thirteen, or fifteen. Now two and two (an even number) means a productive pair; and the one that remains over, remains over for the sacrificer's prosperity. And, moreover, that which remains over for the sacrificer's prosperity is the common property (sa-dhana) of these (others); and because it is the common property of these, therefore they are called Ekadhana (having one as their common property).